1. Field of the Invention
The present invention relates to a contact arrangement for vacuum switches, and in particular to a contact arrangement for vacuum switches having contacts disposed coaxially opposite each other.
2. Description of the Prior Art
Vacuum switches are known having contacts therein which are coaxially disposed opposite each other and wherein a carrier for one of the contacts has a lateral wall forming a cylindrical chamber, with the lateral wall being provided with a spiralling slot so as to essentially form a coil for generating a coaxial magnetic field.
The presence of a coaxial magnetic field in the gap between the open contacts prevents an increase in the arc voltage, and the high power conversion associated therewith. The coil for generating the magnetic field may cylindrically surround the switching chamber and be connected in series with the switch contacts, thereby generating an axial magnetic field dependent on the current which permeates the gap between the contacts. The coil may be constructed multi-ply for increasing the field strength in the contact gap. The manufacture of vacuum switches in this manner, however, requires a relatively high components outlay.
Another type of contact arrangement is known having two essentially cylindrical contacts disposed coaxially relative to each other, with the surfaces of the contacts being in the form of a helical line having the same rotational sense in both contacts, and which are supplied with current in the same direction by the same source as the current which is to be switched. As a consequence of the shape of the surface of the contacts, which is similar to a torsion bar, an azimuthal component of the current is obtained which generates an axial magnetic field between the contacts. The field strength of this magnetic field effects a diffuse arc shape. In order to concentrate this field within the contact gap, the contacts each contain a coaxial core of ferro-magnetic material. As a result of these iron cores, a magnetic field is concentrated in the contact gap which decreases in the radial direction proceeding from the central contact axis. A switching arrangement of this type is described in German OS No. 31 12 009.
Another conventional type of contact arrangement employs substantially shell-shaped cup contacts having contact carriers surrounding a cylindrical chamber, forming the lateral walls of the chamber, and being covered by the contact disk. The axial field is obtained by slanted slots in the contact carriers which are inclined relative to the axis, having the same rotational sense in both contacts. A supporting member is provided between the contact disk and the base of the contact, the supporting member consisting of sheets of ferro-magnetic material which are substantially radially disposed. The supporting member thus also effects a field concentration in the region of the contacts close to the central axis. A contact arrangement of this type is described in German OS No. 32 27 482.